1. Field of the Invention
The present invention relates to a method of removing electrostatically charged particles that are difficult to separate from a gas flow within one or more high-voltage fields, wherein only one high-voltage supply source is used for these high-voltage fields. This is particularly applicable to such particles which by virtue of their physical/chemical properties partly or completely elude the otherwise highly efficient separation in a conventional electrostatic filter or precipitator operating according to the Cottrell principle.
2. Description of the Related Art
As is known, in an electrostatic filter operating in accordance with the so-called Cottrell principle, the charging and transporting of the particles to be separated as well as their deposition on specially shaped precipitation electrodes is carried out in an electrical field, wherein, after an adequate accumulation or agglomeration, the particles are removed from the precipitation electrodes either by mechanical shaking (dry cleaning) or by flushing (wet cleaning). If necessary, several electric fields of the type described above are connected in series with or parallel to each other to achieve the desired overall separating capacity.
The problem of particles that are difficult to separate can be attributed both to the chemical/physical properties of the particles which lead to an insulating layer on the precipitation electrodes and/or to the fact that, due to the electrical flow turbulence or the so-called electrical wind associated with a high current density, as a result of gas ionization in the region between the charging and separating electrodes it is more difficult to deposit on the precipitation electrodes that proportion of the particles which have a grain size of &lt;10 .mu.m. At the same time, it is known that as a consequence of the charging mechanism, namely the so-called impact or field and diffusion charging, a pronounced minimum particle fraction separation output occurs. To counteract the problem of an electrical flow turbulence caused by electrical wind, so-called 2-stage electrostatic filters have been developed, wherein the charging and the separation of the particles is carried out in consecutively connected separate electrical fields. The disadvantage of this method include the required spatial separation of the stages and the supply of different electrical high-voltages.